Quantifying particle coatings using high-precision mass measurements.

We present a general method to quantify coatings on microparticle surfaces based on the additional mass. Particle buoyant mass is determined in a solution with a density that is nearly equivalent to that of the core particle, reducing the magnitude and uncertainty of the measurement. Under these conditions, added material with a different density than that of the core is a larger fraction of the total buoyant mass of the coated particle.

Determination of bacterial antibiotic resistance based on osmotic shock response.

We investigate the buoyant mass of bacterial cells in real time with the suspended microchannel resonator (SMR) as the population recovers from an osmotic shock. The density of the culture medium is chosen such that the bacteria initially have a positive buoyant mass which becomes negative as they recover from the hyperosmotic stress. This behavior can be used to differentiate between an antibiotic-resistant and an antibiotic-susceptible strain of the pathogenic bacteria Citrobacter rodentium, and we propose a general approach for exploiting the high precision of the SMR for rapid detection of antibiotic resistance.

Label-free biomarker sensing in undiluted serum with suspended microchannel resonators.

Improved methods are needed for routine, inexpensive monitoring of biomarkers that could facilitate earlier detection and characterization of cancer. Suspended microchannel resonators (SMRs) are highly sensitive, batch-fabricated microcantilevers with embedded microchannels that can directly quantify adsorbed mass via changes in resonant frequency. As in other label-free detection methods, biomolecular measurements in complex media such as serum are challenging due to high background signals from nonspecific binding.

Teflon films for chemically-inert microfluidic valves and pumps.

We present a simple method for fabricating chemically-inert Teflon microfluidic valves and pumps in glass microfluidic devices. These structures are modeled after monolithic membrane valves and pumps that utilize a featureless polydimethylsiloxane (PDMS) membrane bonded between two etched glass wafers. The limited chemical compatibility of PDMS has necessitated research into alternative materials for microfluidic devices.

Piezoelectric control of needle-free transdermal drug delivery.

Transdermal drug delivery occurs primarily through hypodermic needle injections, which cause pain, require a trained administrator, and may contribute to the spread of disease. With the growing number of pharmaceutical therapies requiring transdermal delivery, an effective, safe, and simple needle-free alternative is needed. We present and characterize a needle-free jet injector that employs a piezoelectric actuator to accelerate a micron-scale stream of fluid (40-130 microm diameter) to velocities sufficient for skin penetration and drug delivery (50-160 m/s).